Process for recovery of metals from their ores



H. v. WELCH. PROCESS FOR RECOVERY 0F METALS FRUM THEIR ORES.

Patented Apr. 27, 1920.

2 SHEETS-SHEET I.

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. APPLICATION FILED AUG-II, T917. 1,338,271.

st-vi H. v. WELCH. PROCESS FOR RECOVERY 0F METALS FROM THEIR ORES.

PPLICTIN FILED AUG-11| 1917- I I I v 2 SHEETS-SHEET 2- A Elecrolyzer .Sump

STATES PATENT- OFFICE.

:HARRY v. WELCH, oF Los ANGELES, .CALIFoRNIAf AssICNoR ToINfr'ERN'A'rIoNAL APRECIPITATION COMPANY, or' Los ANGELES, CALIFORNIA, A CORPORATION-0E CALIFORNIA.

To all whom t may concern:

Be it known that I, HARRY V. WELCH, a citizen of A the` United States, residing at Los Angeles, in the county of Los Angeles, State of-Ca1ifornia, have invented a new and useful Brocess forRecovery of Metals from Their Ores, of which the following `1s a specification,"

This invention.-relates toA recovery 4of metals from their ores, and is particularly intended for the recovery of zinc, the main object of the invention bein to provide for highly efficient recovery o zinc ,or other metal. Another object of the invention is -to eliminate the Waste which usually occurs in zinc roasting operations'by loss of zinc 1n fumes from roasting furnaces. v

For the production lof zinc of high quality, electrolytic processes are now in use, 1nvolving solution of the zinc ore, after preliminary roasting, ifrnecessary, and electrof deposition of zinc from the resulting solution. An important object of the present invention is to simplify the processes or operations required in the production of zinc by electrolytic action.

In order that my invention may be'more fully understood, I will first describe the 'process now -in use for hydro-metallurgy of zinc.4

The ore, commonly a mixture of suliids of the'metals, zinc, iron, lead, etc., etc., is roastl ed usually at as low an 'operating temperature as is practical forv the production of metallic oxid and sulfate. The operating temperature .(usually a low red heat) is maintained at its lowest minimum consistent with properl economic Working of the furnace,-

for the double purpose of, first, preventing the production of acid insoluble compounds .of zinc witheiron and silica, and secondly.,

diminution to the least possible amount of the dust and. fume 'losses carried Vwith and removed by; the furnace'v gases. The so roasted `material -is then charged to tanks containing solution of sulfuric acid, usually in moderate concentration, and by means of mechanical mixing devices, the mixture of solution and ore is kept in continual agitation for a sufiicient interval of time, to-

brin'g into solution the easil `dissolved metallic constituents of roaste ore. The extractionrof the zinc vcontent by .this opera- PRoCEss RECOVERY 0E MET-ALSERCM TIIEIR oREs. l l

tion is seldom complete, 8,0%

eration being considered good, an in cases vwhere furnace capacity has been sought by l 1 t. gan Op 55 Speci-cation of Letters lPatent Patented Apr, 27, 1920,

Application led August 11, 1917. Serial 110,185,778.`

increasing roasting temperature, the extraction may fall to or even lower.`

The extraction'by acid leach upon the roasted mixed sulfd ores' or concentrates, not only brings into solution the zinc constituent, but as well, the' partial or complete solsulfate constituents, lsuch as Fe, Cd, As and Sb, which may be present either-,in con- `lution of the many-'other metallic oxids or l siderable quantities like the iron, or minnte amounts, like the Cd, A s and Sb, but

usually must be completely removed in the,

'final purification of the solution for the electrical deposition, cells. The solution and pulp, 4following tank leaching, are then separated by decantation oriltration, eitherA before or after the precipitation ofthe dissolved iron by lime. The neutral solution resulting as filtrate during removal of the Fe, etc., is treated with" finely divided me# tallic Zn or ZnO for displacement and pre'- cipitation l,of all metallic constituents of lower solution pressure than the zinc, but especially for the removal ofthe (ldcontent. Theperiod of treatment required for tion, and as well, the diiculties inherent in the filtration of such colloidal or like precipitates as ferric hydrate, Fe2 (0h16),

' make the process one of extended operation,

and while the leaching of the zinc and other constituents from mixtures of gan ue andl land restricts-to a Very material degree, the

3 the production and purication of the soluamount of wash water which may be used,H

in freeingthe extracted residue 'from its pregnant zinc solution.

According to my invention, thel zinc ore is roasted under such conditions as to vola-.

tilize as much as possible of the zinc, and the zinc so volatilized is .allowed to burn while in the Avapor phase, producing 'fume-of solid zinc oxid.v Suclf oxid fume is precipitated or collected, preferably by,elec`trical precipitation, and is subjected to laction of a solvent liquid, preferably concurrently with its precipitation. orcollection, and the resulting sol,

` of the material, andl with means for rotation of.

paratus suite lation, after .removal of all sus ended material, is treated for separation o othermetals than zinc, and is then= electrolyzed for recovery of the zinc. The barren solution resultin #from such electrolysis is preferably reuse as solvent liquid in cyclic repetition zinc oxid fume or dust.

yThe accom anying drawings illustrate aplble for carrying out my process and referring thereto:

igure 1 is a dia rammatic elevation of such apparatus part y in section.

Fig. 2 is a vertical section of another form of the apparatus, for volatilizing zinc from its ores.

Fig. 3 is a side elevation of a modified apparatus -for carryingl out my invention.4 j The apparatus s own in Fig. 1 of the zinc from the purified' solution to the leachin'stage o fthe process.

he roasting Ameans 1 may consist of-a rotary drum ortube, provided with suitable means for'rotation thereof, and provided with means for supplying zinc ore thereto, together withV coal or other carbonaceous said drum, said drum communicating with flue 3 in such manner asto discharge into the latterthezinc fumes produced, and to admit, for example, at the joint 40 between the drqni and Hue, sufficient air for oxidation o the zinc. volatilizingjand oxidizing -the zinc may vbe used-for'example, a bedded charge 4furnace asshown at 11 in Fig. 2, provided with a grate 12 for supporting the `charge of ore and coal,with a blower 13 for forcing air below saidA grate and withvfume inlet 14 opening'into flue 3, with provision for air su'. ly as 4shown at 15. l

; e .electrical precipitator 2 as shown in the drawing, comprises vertical ilues 6, preferably. formed asi vertical passages in a monolithic concrete structure, said structure havin sidewalls 7, and vertical partitions 8- ividing the .space 'between said walls so as to vform said verticall flues, and

Vso

said flues being round or rectan ular in cross-section as may be desired.4 n inlet header 9, communicating with flue 3, is rovided at the upper endof said flues an an outlet header' 10 is provided below said flues and communicates with an outlet flue 17. The lower part of lower'headerflO ma be process on a further quantity of the 'above said header.

Any .other means for 'divided by .partitions "into" a plurality of Asump chambers 18,` for receiving the li uid ported, for example, b .insulated frame 19,

n on vertical ro s 2,0` extending upwar l through insulating plates 21 in the top o the upper header and connectedto a horizontal frame 22 resting on insulators023 Said discharge electrodes may consist of wires 25 suspended from hangers 26 carried byframe 19 and connected at their lower ends to a plate or weight 27. The walls of each flue 7 are preferably 'inclined upwardly -so as to converge downwardly so as' to produce better distribution of liquid therein, and the dis- .charge electrode members 25 also preferably converge downwardly so as to be approxi'- mately parallel to the opposingwalls.`

Suitable means, such as nozzles 30, 31, 32. are provided for vsu plying acid solution or other solvent liqui to the-upper parts of the respective flues 6. Pumps 33 and. 34 and pipes 35 and 36 are provided for forcing the liquid from each sump chamber 1S at the bottom of a precipitator flue, tothe. top of another precipitator flue, sopas to subject the liquid to a series of exposures to the gas. Cooling tanks 37 may be provided, if required,- for cooling the li uid passing through pipes 35 and 36. Sai pipes may be arranged to drawliquid only lfrom the v being provided for drawing' oif sediment upperpart of chamber 18, other pipes .39

from the lower part of saidy chambers and conducting the saine to `filter 40, or else-` where,.as re uired.

From the ast sum chamber 18a` pipe 38 leads to a series o devices, for separating impurities from the liquid, said series including filters 40, 41, 42'and agitators\43, 44 interposed betweenk successive filters for agitating the 1i uid with suitable reagents, t e last filter dischargin into a sump iiitablepipin -is provi ed for connecting said series of evices, and a by-pass 46 may befprovided for each filter. Said filters may be of any suitable t andif desired, de-

.cantation tanks may e `used in place thereofor in conjunction therewith.

A pump 48 forcs liquid from sump'45 through pipe 49 to a regnant solution tank 50 from which the. iqu'id is delivered as required to an electrolyzer- From said electrolyz'er,barren solution is pumped by pump 52,` through. pipe 5 3 tolstorage'ptanks 54, whence the solution is delivered as reuired, through p ipe 56 tothe nozzle 30 or' one of the precip'itator flues. 6.' The walls of -lues 6, constitutirrcollecting elec-l trodes are grounded, as in icated at 58, the stream of solution therein givingtlie conductance required for the electrical-'pre` solid zinc oxid fume, .which is cipitation operation.v The discharge electrode system is connected by wire 59 to any suitable means forsupplying high tension current thereto--for example, such as described in-patent to -F G; Cottrell, No. 895,729--August 11, 1908.

-My process maybe carried out in the ferent ways-for example, the carbonate or oxid ores may be mixed with'coal, `sufficient in quantity to provide upon combustion, a strictly reducing atmosphere and temperature sufficient to volatilize the reduced zinc, and a quantity of a'ir or oxygen may then be introduced in the gaseous exits from furnace, sufficient to render the resulting 'gaseous mixture, oxidizingvin character. furnace construction used may follow the type shown in Fig. 2, of heap roasting or beddedl charging on vstationary grates, with blower discharging beneath grates, etc., or

furnaces of producer gas type and form,

or the type of continuously rotating cylindrical furnaces, of the cement kiln type, as shown in`ll`ig. 1, said furnaces being, for example, 100 or more feet in length.

Or, the calcined mixed sulfids, of possi# bly Zn, Cu, Pb, Fe, etc., may supply the feed to a reverberatorywith reducing .atmosphere, or to an electrically auxiliary heated reverberatory, and as in the previous method, the furnace effluent gases being converted to oxidizing nature by admixture ofv air, either justvbefore the final exit from furnace, or in flue'leaving furnace.

Or, the raw sulids may Ibe smelted directly in converter type of furnace', thus se curing essentially the separation of Cu and Fe from the Pbfand Zn; the first two r'emaining essentially in the converter, Cu in f its metallic state, and the Fe as ferrie oxid vand iron silicate, while the Pb and Zn both appear essentially as 'fumes of oxidand sulfate in the converter gas effluents v The furnace effluent gases carrying in susl' pension as fume, essentially all the Zn 1and Pb constituents of the original furnace feed, togetherl with a certain 'quantity of'dust of Cu, Fe, etc., and of the gangue, and normally, quantities of the acid' gases of sulfur, pass directly, land While still at a high temperature, to the electrical recipita'tor 2,

the collecting electrode of w ich is essentially a flowing sheet or film of .the barren zinc solution, vreturning from `the lzinc? elec- The l trol by any of the usual forms of electrode devices, such as p1pes, plates or rectangular boxes, etc., used lin the art.

trolytic depositing cells.l This flowing elece medium may be confined or directed .In the electrical precipitator, the zinc oxid fumes and other solid material suspended inthe furnace effluent gases, are precipitated onto the said stream -film or Vsheet of. liquid, with` the acid and cohtinuallycarried away by `such'stream and the body of liquid containingV theprecipitated material, is collected in the sump chamber 18. By precipitating the zinc oxid fume from hot furnace gases directly onto the body of solvent liquid certain advantages are obtained as hereafter .set forth:

In the present day development ofthe f art and practice of electrical precipitatien of metallic fumes by the procedure disclosed in patent lof F. G. Cottrell above rel lferred to, the .effectiveness of the precipi-itation has been found to vary greatly w1th the nature of the metallic fumes encountered, .and its physical condition. Zinc oxid fume has shown both lin laboratory tests and field operatiomthat very special conditions must be maintained to secure its `proper precipitation and that in gases and collecting electrodes where the existing teniperature is over 100o C., the precipitation is usually difficult, due largely to the unfavorable electrical eff'ects of the deposited zinc oxid fumes. These unfavorable eects ap.- pear in two ways, andl are'more marked with increasing deposit of zinc oxid fume,` and while they are not peculiar lto Zinc oxid fume, laboratory work and field experiment have shown Zinc oxid fume in dry condition, to be one .of the most difficult substances to precipitate on account of its electrical effects.' One seriously vdetrimental effect is ldecreasing first the high potential which may be carried. across the treater terminals without undue arcing over,'z'. e.,- the. arc' ing' voltage.7 F or example, in a special case, I have recorded a 90,000l volt reading across the terminals with carefully cleaned collecting electrode, while a deposit by electrical precipitation of not over ,Jg zinc oxid fume upon the collecting electrode (4 to 5 grams per square foot) lowered the potential which could be maintained with only an occasional snap over to some`46,000 volts. A second effect is that the dry Ideposit of zinc oxid fume (and various other fumes that as in a special case cited, as a zinc oxid fume deposit` approached the value of 4% to 5 grams per square foot of collecting electrode area, the 4current approached the zero value, andthe efficiency of precipitation is vlnaturally decreased. f- Within the'. electrical precipitator, the following. continuous conditonsand opera-l also) acts as an insulator, with the resul-t ltions prevail: viz.-a prompt and effective precipitation of the dust and fume u on the liquid collecting electrode vby the high p0.- tential discharge, due in a large measure, to the absolutely uniform electrical field prevailing, since the equivalent of a clean receiving electrode is continuously maintained y by theflowing electrolyte acting as a collectingl electrode medium. Second, an obsorption of heat from the gases, rendering the solution exceedingly chemically active. The amount of heat absorbedis proportional .to the temperature difference between the gases and the collecting electrode medium,`

their relative volume and velocity, the ratio of collecting electrode surface, to cubic vol-l ume of treater unit, etc., and the treater unit dimensions are to be so chosen as to heat requirements, as to provide' the best of working conditions. fIn general practice, th1s type of apparatus permits of larger Working units, and higher impressed lotential than in common practice today. hird, due to the acid character ofthe solution, and its increased chemical activity, due to increased temperature, and the fact that under the influence of a high potential field, there is an apparent decrease in surface tension, "the fumes, and as Well, the soluble dust precipitated, are immediately and vigorouslyl attacked by the acting collecting electrode flow. Fourth, from sulfid ores,

`and under the in uence o the furnace effluent gases will contain conf siderable quantities of the acid gases of sulfur, and these inv art, may be absorbed, an oxidizing agent in the collecting electrode medium, such as a manganate or permanganates, the unstable sulfites may be converted to those of stable sulfate character. Y p By returning the solution from the sump vchamber of certain of the recipitator flues, to the other precipitator ues, the solution may be exposed repeatedly to the stream of material being. precipitated so that the'concentration of zinc salt in the solution `may be increased to an requiredv extent. In

such case, the oxidizing agent, such asl a salt of Mn is oxidized at the anodefof the electrolytic zinc depositing' cells and is in the solution returning from the cells, andi-, is available to oxidize during the periodwhile the solution is functioning as the col4 lecting electrode medium, in the electrical precipitation treater, the sulfite'v formed, or absorbed on the ,collecting electrode. By

this means, a continual production'v of H,SO4, orits equivalent in sulfates, is-pro` l. duced, sufficient to 'take care of theloss, due' to the removing of impurities and neutraliization of solution for electrolytic zincA defvpositing cells, and b this means, the addition of. extraneous l tice, in cost and volume both large,'v1s, in the Vma1n,'avo1ded. v.

. most Wholly 2SO4 in present prac-f' The liquid soliltion passing the electrical precipitator, the solution now containing in solution besides the zinc, some lFe, Ud, etc., and in suspension, Pb SO4` and insoluble dust, is filtered in filter 40, treated in agitator 43 with lime to precipitate iron which is then filtered out in filter 41, the filtrate being then treated with zinc in agitator 44 to precipitate cadmium, etc., and the final filtered and purified Zn solution passed to the electrical zinc 'depositing cells, and returns thence from these cells as an essentially barren zmc solution, and acid 1n' character.

Thus, the solution moves essentially incyclic` flow between lie collecting electrode of the electrical pre ipitation treater umt, and electrical zinc `precipitating cells.

In some cases, it may be desirable to sub ject the fume bearing gas to more than one ply -means for distributing solvent liquid on the collectin electrodes. Said precipitators are provide respectively with sump chambers 65 and 66, having discharge gates 67 and`68 for sediment or sludgefand overflow or decantation pipes 69-and 7 0l for clear liquid. Substantially all the heavy' dust -may be removed from the gases in the first precipitator and may be removed through discharge gate67, so that the fume passing to the second precipitator ma ,consist alvof zinc oxid. ipey 69 conducts the c ear liquid from' the first sump 65 to an agitator 71 where it may be treated with lime for precipitation of iron, which is filtered out infilterl 72, the filtrate pass? ing to a sump 73.. Decantation pipe 70 may also conduct theclear liquid from recipi tator sump chamber 66 to sump 3, and liquid may beforced from said sump by pump 74 through pipe (5 to a storage tank 6, whence it flows; to the distributing pipe 77 for the second .precipitator, so that the solvent liquid moves in a cycle between the precipitator 63 Aand sump 73, whereby a gradual accumulation .and concentration of lzincv sal/t in the liquid may secured. The heat of the gases causesv heating and evaporation` of the liquid as it is being circulated .inthis manner and thus accelerates the concentration,and at the same time, the'heating of the liquid 'makes it more active chemically and increases its .solvent action inthe zinc contents ofthe fume precipitated with it by electrical action inthe pre cipitator. A portion'of the concentrated liquor is withdrawn from this leaching cycle to an agitator 8O fortreatment'with a precipitating agent for removalof iron, and' the resultant solution is filtered in filter 81 turned by pump '83 and pipe 84 to a storage tank 85 supplying the solution feed means 86 for the first precipitator. Filter 81 may ing or collecting means.

have wash watery supply `means 86, the

vwashings being delivered b pipe 87 to a 'sump 88 which receivesthe ltrate from filter 81 and-supplies itto the electrolyzer.'

The process is .also applicable to other metals than zinc-for example, lead ore may be roasted to produce lfume of leadoxid and such fume may be collected, preferably in an`v electrical precipita-tor, in a body of alkali solution, vthe .lead being recovered Afrom such' solution by electrolysis and the barren solution returned to the precipitat- .While I prefer to employ electrical precipitation and the process offers certain ad vantages as above set forth in connection with electrical precipitation, it is applicable, in some cases, in connection with collection by mechanicalmeans such as scrub-v bers washers, etc.

The typical embodiment of the process is that in which substantially all, or the major portion of the mineral, such as zinc, to be recovered is volatilized and then precipitated as abovedescribed, as such application of my invention presents decided advan.

tages in simplicity of operation andl efficiency of recovery. However, in some cases, the invention may beI applied with advantage to the recovery of metals from waste fume gases produced incidentally in the operation of roasting, sintering, smelt in or converting apparatus.

yinvention may also be applied with.

advantage to the recovery of sulfur and separatlonv of zlnc from fumes coming from lead ore slntering machines. In sintering lead, it is usual tolimit the amount of pyrites that may be used, so as to avoid eX- cessive amount of sulfur in the fumes, which isa source .of danger when bag-houses are used, by reason of the liability of its setting fire-to the bags, and is also objectionable when dry electrical precipit'ators are used, as the dry, highly insulating deposit of sulfur on the electrodes ofthe precipitator, interferes with the successful operation thereof. By passing the fumes from sintering apparatus through an electrical precipitator, in the manner above described, with flowing liquid electrodes, the sulfur' is precipitated..satisfactorily in moist condition and is continually carried away, so that it does not interfere with the electrical operation. n important advantage of my process, in this connection, is that ores may be utilized -which contain relativel high per centages of pyrites, and whic are ordinarily unavailable for that reason. The

sludge resulting from precipitation of the `dust and fumev into said solution may be treated for separation of sulfur and zinc therefrom. In this case, the solution (for example, dilute sulfuric acid) used in washing the receiving electrodes of the preclpitator, will be adapted to -dissolve zinc,` andl vided, removing the. sulfate radical as CaSO4, and the zinc hydrate is then precipitated by milk of lilnell The resultingr solution of calciumghlorid may then be used on a fresh batch 'of ZIISO,l solution in cyclic operation. i .The residue resulting from filtration of the filter sludge is dried, for example, in a rotary steam drier, and then subjected to treatment with carbon bisulfid, in digesters operated in cyclic and counter current manner for solution and removal of elemental sulfur content Athe pregnant solution then passing to b ot waterheated evaporating pans for recovery of sulfur and distillation of the CS2, the latter being condensed in suitable condensers and returned to the sulfur extracting cycle. The residue from which sulfur has been extracted is returned'to feed of the sintering machine. j

What I claim is: Y

1. The process of recovering a metal from its ores, which consists in subjecting the ore to the action of heat and a suitable reagent to produce a fume containing said metal passing the gases containingfsaid fume 1n Contact with a body of liquid capable o f dissolving said metal in the fume, preclpitating said fume into said bodyof liquid by the action of an electrical field, subjecting the solution resulting from the action of said liquid on the fume, to'treatment for separating the fsaid vmetal therefroml and utilizing the remaining liquid in cyclic repetition of the process to act on a fresh quantity of fume.

2. The process of separating zinc from an ore thereof, which consists'in volatilizing the zinc from the ore in such manner as to produce a zinc bearing fume and` pr e cipitating such fume'into a body of liquid by then action of an electrical field.

3. The process of separatin zinc from anA ore thereof, which consistsy 1n volatilizing ment of the liquid.

4. The process-of separating zinc from an ore thereof which `cons1sts in volatilizingthe zinc in metallic form, oxidizing the zinc vapor to roduce zinc oxid fume precipitating suc fume by' the'action of an electrical field, into a -bod -of liquid ca able of dissolving zinc lthere m, 'and su jectingthe resultingsolutionfto treatment to first remove suspended material and other impurities therefromgand tothen separate thev zinc therefrom.

5'. The process of recove "-zinc''froi .a

' suliid ore thereof, which conslsts in heating the ore in the 'presence of vsuitable reagents to produce metallic zinc vapor to ether with,

` acid bearinggases, oxidizing. suc vapor to produce zinc oxid fume mixed with acid bearing gasesz subjecting the fume to elec-- trical action 1n contact with a` liquid containin water in such manneras to. cause preci ltation of the fumein said liquid, ab,-

sorption of acid from said gases, and solu- `tion of zinc from the preci itated fume in said liquid by the action osuch acid, and se arating zinc from the resulting solution;

n testimon vwhereof "I have hereunto set' my. hand, at `3rd day ofAugust, 191

ls Angeles, California, this HARRY v. WELCH. 

